mcabber: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/mcabber - from package: mcabber

You may install the required package with command apt-get install {package}
Error in other languages:
mcabber: bevel nie gevind nie
mcabber: comandă negăsită
mcabber: comando não encontrado
mcabber: commande introuvable
mcabber: command not found
mcabber: käsku ei ole
mcabber: không tìm thấy lệnh
mcabber: komanda nerasta
mcabber: Kommando nicht gefunden.
mcabber: kommandot finns inte
mcabber: komut yok
mcabber: nie znaleziono polecenia
mcabber: níor aimsíodh an t-ordú
mcabber: no se encontró la orden
mcabber: no s'ha trobat l'ordre
mcabber: opdracht niet gevonden
mcabber: parancs nem található
mcabber: perintah tidak ditemukan
mcabber: príkaz nenájdený
mcabber: příkaz nenalezen
mcabber: команда не найдена
mcabber: командата не е открита
mcabber: 命令找不到
mcabber: コマンドが見つかりません